You should lager at 0 psi. It may build up a little pressure from the yeast, but vent it now and then (once a week or so). When you're ready to serve, pressurize it to the appropriate pressure for the amount of carbonation you want.

I have lagered beer both ways but now I pretty much do like Pete does.

Cannot remember where I go this from:

Traditional Beer Lagering

Lagering beer was developed in Germany for bottom-fermented lagers, and it involved a long, cold storage between 1 and 3 months in conditioning tanks. Today the trend is for shorter storage times of between 2 and 3 weeks at higher temperatures, to free up tanks. However, the shorter lagering programs can result in beer with higher levels of yeast and haze, requiring subsequent clarification steps.

Accelerated Beer Lagering

Traditionally, lagering served four purposes: extract reduction, clarification, carbonation, and flavor maturation. However, given the capital-intensive nature of storage, many brewers have reduced the storage time and downsized the required plant facilities. Today, with better equipment obviating the need for secondary fermentation, the wort is usually fully attenuated during primary fermentation, thereby eliminating the need for traditional lagering. The beer is usually conditioned between 2 and 5 days at temperatures ranging between -1 and 2 degrees C before filtration.

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Everything You Ever Wanted To Know About Lagering (And REALLY Wanted to Call Up Kev To Find Out)

Lagering is the delicate little sister to the brutish ale. Lagers takes their sweet time getting ready, they're soft and silky, clean and smooth; ales, on the other hand, are complex and in-your-face, full of depth and roughness, and edginess that makes you wonder what REALLY makes them the way they are. Lagers are easy to caress on a hot summer night, ales are good for slamming on a table and wiping away with the back of your hand.

Both are great to make and even better to drink. But be forewarned, O My Little Ones, lagers are the tortoises of the beer world, going slow and steady until the race is won. Ales, being the little rabbits that they are, sprint ahead and are ready to drink in one-third the time it takes to produce a gentle lager. But, as much as I like ales, (and, oh, do I!!), there is something very special about pouring a nice frosted lager into a tall, thin glass on a hot day. Here is the scoop on producing your very own:

First, know this: lagers come in every shape and color. Dunkels are pitch black, dopplebocks are brown and strong and malty, Oktoberfests are amber and balanced, pilsners are golden yellow, dry and hoppy. Just like ales, lagers run the gamut, and for every ale, there is a counterpart lager. (Porter and dunkels, Scotch ales and dopplebocks, Amber ales and Oktoberfests, pale ales and pilsners.) So, be not general when asking to make a lager. They are all doable.

Boil the beer and cool it down as normal. If you are doing a yeast starter culture, skip ahead a few paragraphs. Starter cultures for lagers are great to do, but by no means necessary. If you are NOT doing a yeast starter culture, after the beer has dropped down to 80 degrees or less, add your packet of lager yeast (we almost always prefer liquid lager yeast to dried yeast, but both forms are available). KEEP THE BEER WARM (INSIDE THE HOUSE) FOR 12 TO 24 HOURS. You must wait until you see activity in your fermenter before moving it out to a cold spot. Moving it outside too quickly will prevent your beer from starting fermentation, and it will eventually spoil.

Once you see foam on the surface of your beer, and your airlock is percolating, immediately move your beer out to a 42 to 58 degree environment, 45 to 55 degrees is optimal. The activity will slow down but should continue to bubble steadily for the next few weeks.

If you HAVE done a yeast starter culture: after the beer has dropped down to 80 degrees or less, pitch your starter solution into the fermenter. You should try to pitch AT LEAST one-half gallon of starter into a five gallon batch. Less volume gives you much less advantage, so I usually wouldn't waste my time to produce a 12 ounce bottle of yeast starter. IF you have pitched one-half gallon of starter into a five gallon batch, immediately move the beer out to a 42 to 58 degree environment, 45 to 55 degrees is preferable. The activity should start within 24 hours.

OK, in either case, the beer is now out in the cool area, fermenting away slow and steady. You usually will not see the violent, volcanic craziness of your typical ale fermentation. The activity is almost..... "dainty." (Whatever, Kev...) OK, so, as The Beatles would say: let it be. Check on it once a day or so, to make sure the cat, or the raccoons, or whatever don't knock off the airlock, and just let it ferment away.

Do not let the temperature get much below 45 degrees, if you can help it. Eventually, the activity in the airlock will slow down to one bubble every three to four minutes. This is MUCH longer between bubbles than your typical "90 second" rule that you use for ales. Listen, boys and girls: for lagers, it is better to be one week too late in transferring to secondary than to be one day too early. Just let it be.

Eventually, when the activity level is very slow, rack the beer to a glass secondary. You have the option of moving it into a warm (60 degree) environment for a few days BEFORE racking, in order to finish off the fermentation and perform what is known as a "diacetyl rest." But it is not necessary, and may be more bother than it is worth. In any case, once the beer is transferred to secondary, let it sit at the same temperature that it has been at for at least one week more. You should see no activity in the fermenter by the end of that week.

Then, either leave the beer in that same chilled area for another four to eight weeks (longer is better), OR put the fermenter in a refrigerated (35 degree) environment and let it sit for three to four weeks.

At the end of that resting (lagering) period, it is time to bottle. If the beer has been in secondary for longer than eight weeks, you may want to add a fresh yeast at bottling - this will ensure a healthy bottle conditioning. If it has not been that long, the remaining yeast (invisibly suspended) in the beer will usually do the trick.

Bottle the beer as normal, and let them sit in a 60 to 65 degree environment for one week. Then move the bottles to a 45 to 55 degree environment for 4 to 6 weeks. By the end of that time, they should be fully carbonated. Call or e-mail with questions or troubles.,...... Beverly Beverly Beverly... Bark Like a Dog Dear Beverly

Pete, I want to give the yeast every chance they have to ferment out cleanly. Carbon dioxide isn't good for the yeast and should be vented IMHO. In my eyes, there's no harm in venting, and there could be harm carbonating. Besides, 20psi at say 40F would give you about 3.2 volumes of CO2, that's a lot of carbonation.

Yep, 20 psi then disconnect as Paul mentions. With the small amount of headspace in a full corny, that usually gets absorbed pretty quickly. I'll repressurize every so often.

I also forgot to mention in my first post, that I pressurize only if I'm sure the beer is truly done fermenting. I personally don't lager to trim off the last few gravity points, but rather to let the flavors come together and smooth out a bit.

Many commercial lager breweries "cap the tank" near the end of fermentation (or after the kräusen beer is added) to retain natural carbonation. The beer is then lagered with (roughly) the target volumes of CO2 dissolved in it.